Heretofore, various types of brushless motors have been known and devised in the industry. In such motors, the stator windings must be supplied with electric power in the appropriate sequence in order to produce rotor shaft torque. It is known to use Hall effect devices to sense rotor position and to thereby control the excitation of the stator windings through appropriate control and switching circuitry. Hall digital switches, excited by magnetic flux changes, have been used to create the signals to provide the correct sequence for power application to the stator windings from an electronic controller to which the Hall digital switches are connected. A suitable Hall effect device is the bipolar Hall effect digital latch shown in Engineering Bulletin 27608 of the Semiconductor Division of Sprague Electric Company of Concord, N.H. As with most such Hall digital switches, these devices require the sensing of certain flux densities in order to switch and thereby provide the proper output voltages to the circuits of the electronic controller connected to the stator windings.
In operation of brushless motors, it has been found that if the available flux densities are not sufficient to actuate the Hall effect switch, electronic power output semiconductor devices of the controller will not switch on and off properly. This will cause them to draw high currents considerably beyond their capacities, resulting in their ultimate failure. Further, transient flux fields from stator conductors and core sections have also been found to cause false switching of the Hall ditigal switches, again resulting in improper operation of the controller circuitry and ultimate destruction of the same. In summation, it has been found that the Hall effect sensors or switches used in brushless motors must be maintained within a strong magnetic path of low reluctance, while being shielded from stray flux present within the environment of the motor itself.
The aforesaid problems inherent with brushless motors have been aggravated by the fact that the rotating magnets of such motors, coupled with the flux conduction through the stator core generates a dynamic flux field which is difficult to shield or control. Additionally, attempts to reduce the size of the packaging of such brushless motors inherently places the stator windings close to the switches themselves.